linux-kernel - Re: [PATCH v3] media: rc: ir-spi: allocate buffer dynamically

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aEf9b17JU1a5q2hC@gofer.mess.org>
Date: Tue, 10 Jun 2025 10:39:59 +0100
From: Sean Young <sean@...s.org>
To: Cosmin Tanislav <demonsingur@...il.com>
Cc: Mauro Carvalho Chehab <mchehab@...nel.org>, linux-media@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] media: rc: ir-spi: allocate buffer dynamically

On Mon, Jun 09, 2025 at 02:17:13PM +0300, Cosmin Tanislav wrote:
> Replace the static transmit buffer with a dynamically allocated one,
> removing the limit imposed on the number of pulses to transmit.
> 
> Calculate the number of pulses for each duration in the received buffer
> ahead of time, while also adding up the total pulses, to be able to
> allocate a buffer that perfectly fits the total number of pulses, then
> populate it.
> 
> Signed-off-by: Cosmin Tanislav <demonsingur@...il.com>
> ---
> V3:
>  * move the allocation to be done per-TX operation
> 
> V2:
>  * use devm_krealloc_array
> 
>  drivers/media/rc/ir-spi.c | 33 ++++++++++++++++++++-------------
>  1 file changed, 20 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/media/rc/ir-spi.c b/drivers/media/rc/ir-spi.c
> index 8fc8e496e6aa..50e30e2fae22 100644
> --- a/drivers/media/rc/ir-spi.c
> +++ b/drivers/media/rc/ir-spi.c
> @@ -21,13 +21,11 @@
>  #define IR_SPI_DRIVER_NAME		"ir-spi"
>  
>  #define IR_SPI_DEFAULT_FREQUENCY	38000
> -#define IR_SPI_MAX_BUFSIZE		 4096
>  
>  struct ir_spi_data {
>  	u32 freq;
>  	bool negated;
>  
> -	u16 tx_buf[IR_SPI_MAX_BUFSIZE];
>  	u16 pulse;
>  	u16 space;
>  
> @@ -43,37 +41,42 @@ static int ir_spi_tx(struct rc_dev *dev, unsigned int *buffer, unsigned int coun
>  	unsigned int len = 0;
>  	struct ir_spi_data *idata = dev->priv;
>  	struct spi_transfer xfer;
> +	u16 *tx_buf;
>  
>  	/* convert the pulse/space signal to raw binary signal */
>  	for (i = 0; i < count; i++) {
> -		unsigned int periods;
> +		buffer[i] = DIV_ROUND_CLOSEST(buffer[i] * idata->freq, 1000000);
> +		len += buffer[i];
> +	}

This looks great, thank you.

I do have one concern though. If someone sets a carrier of U32_MAX - 1 then
this code could be doing largish allocations, spending too long in kernel
space filling them with data and spi can't send it anyway. Actually
the kmalloc might fail which doesn't look good in the logs.

We may have to constrain the carrier to something spi can handle.


Sean

> +
> +	tx_buf = kmalloc_array(len, sizeof(*tx_buf), GFP_KERNEL);
> +	if (!tx_buf)
> +		return -ENOMEM;
> +
> +	len = 0;
> +	for (i = 0; i < count; i++) {
>  		int j;
>  		u16 val;
>  
> -		periods = DIV_ROUND_CLOSEST(buffer[i] * idata->freq, 1000000);
> -
> -		if (len + periods >= IR_SPI_MAX_BUFSIZE)
> -			return -EINVAL;
> -
>  		/*
>  		 * The first value in buffer is a pulse, so that 0, 2, 4, ...
>  		 * contain a pulse duration. On the contrary, 1, 3, 5, ...
>  		 * contain a space duration.
>  		 */
>  		val = (i % 2) ? idata->space : idata->pulse;
> -		for (j = 0; j < periods; j++)
> -			idata->tx_buf[len++] = val;
> +		for (j = 0; j < buffer[i]; j++)
> +			tx_buf[len++] = val;
>  	}
>  
>  	memset(&xfer, 0, sizeof(xfer));
>  
>  	xfer.speed_hz = idata->freq * 16;
> -	xfer.len = len * sizeof(*idata->tx_buf);
> -	xfer.tx_buf = idata->tx_buf;
> +	xfer.len = len * sizeof(*tx_buf);
> +	xfer.tx_buf = tx_buf;
>  
>  	ret = regulator_enable(idata->regulator);
>  	if (ret)
> -		return ret;
> +		goto err_free_tx_buf;
>  
>  	ret = spi_sync_transfer(idata->spi, &xfer, 1);
>  	if (ret)
> @@ -81,6 +84,10 @@ static int ir_spi_tx(struct rc_dev *dev, unsigned int *buffer, unsigned int coun
>  
>  	regulator_disable(idata->regulator);
>  
> +err_free_tx_buf:
> +
> +	kfree(tx_buf);
> +
>  	return ret ? ret : count;
>  }
>  
> -- 
> 2.49.0
>